1. Field of the Invention
This invention relates to a damper apparatus used to absorb a sudden torque fluctuation in a torque converter with a lock-up mechanism for an automatic transmission of a vehicle.
2. Related Background Art
Generally, a torque converter transmits power through a fluid and can therefore realize smooth running. But it suffers from the disadvantage that fuel consumption is increased due to the energy loss attributable to the slip of the fluid. To solve this, recent torque converters are provided with a lock-up mechanism.
The lock-up mechanism is a mechanism which comprises a lock-up clutch having a frictional surface and in which, when the vehicle speed becomes a predetermined speed or higher, the flow of a fluid in the torque converter automatically changes and urges the frictional surface of the piston of the lock-up clutch against the front cover of the torque converter to thereby directly connect an engine and drive wheels together. Thereby, the influence of the slip of the fluid is eliminated and an improvement in fuel consumption can be achieved.
In such a torque converter, a damper apparatus comprising a plurality of springs is provided to absorb a sudden torque fluctuation from the engine when the piston (lock-up piston) of the lock-up clutch becomes fastened to and liberated from the front cover of the torque converter.
For example, in a damper apparatus disclosed in Japanese Laid-Open Patent Application No. 5-172185, a ring-molded retainer plate and the flange of the outer diameter of a piston are curled to thereby hold a spring. The spring is contained in a spring holding portion molded on the retainer plate and the flange. Also, in a damper apparatus 100 for a lock-up clutch according to the prior art shown in FIG. 6 of the accompanying drawings, a spring 120 is held by only a retainer plate 110.
Generally, when manufacturing the retainer plate the yield of its material is poor because of ring molding, and a complicated drawing process is required. Also, high accuracy of press working is necessary due to the adverse effect of quenching distortion or the like. The shaping of the outer diameter of the piston is also complicated. Also, a novel design has been necessary for the change of the characteristic of spring recombination and a lock-up clutch having a different diameter. Particularly, in the prior art as shown in FIG. 6, the retainer plate receives a spring load in a cantilever fashion and therefore, in the setting of a high load, damage has sometimes occurred from the seam between the load transmitting portion and the spring holding portion of the retainer plate.
The retainer plate and a guide member covering the spring are integrally pre-assembled to provide a unit, and the unit is disposed in the piston by a necessary torque capacity. Also, the unit holds a plurality of springs disposed in series.
It is an object of the present invention to provide a damper apparatus for a lock-up clutch in which springs of the same type can be mounted on individual lock-up clutches of different diameters and a unit enables the springs to be disposed in series depending on a set characteristic and a unit construction is provided, whereby spring holding structure becomes strong and a high capacity is obtained by a small number of parts and the degree of freedom of disposition is improved.
To achieve the above object, the present invention provides a damper apparatus for a lock-up clutch in which a spring is disposed on a lock-up piston, comprising:
a retainer plate containing the spring therein; and
a guide member provided in opposed relationship with the retainer plate for holding the spring with the retainer plate;
characterized in that the retainer plate and the guide member are made integral with each other with the spring interposed therebetween and are constructed as a damper unit.